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首页> 外文期刊>Journal of Molecular Biology >Role of counterion condensation in folding of the Tetrahymena ribozyme. II. Counterion-dependence of folding kinetics.
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Role of counterion condensation in folding of the Tetrahymena ribozyme. II. Counterion-dependence of folding kinetics.

机译：抗衡离子缩合在四膜虫核酶折叠中的作用。二。平衡动力学对折叠动力学的依赖。

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Condensed counterions contribute to the stability of compact structures in RNA, largely by reducing electrostatic repulsion among phosphate groups. Varieties of cations induce a collapsed state in the Tetrahymena ribozyme that is readily transformed to the catalytically active structure in the presence of Mg2+. Native gel electrophoresis was used to compare the effects of the valence and size of the counterion on the kinetics of this transition. The rate of folding was found to decrease with the charge of the counterion. Transitions in monovalent ions occur 20- to 40-fold faster than transitions induced by multivalent metal ions. These results suggest that multivalent cations yield stable compact structures, which are slower to reorganize to the native conformation than those induced by monovalent ions. The folding kinetics are 12-fold faster in the presence of spermidine3+ than [Co(NH3)6]3+, consistent with less effective stabilization of long-range RNA interactions by polyamines. Under most conditions, the observed folding rate decreases with increasing counterion concentration. In saturating amounts of counterion, folding is accelerated by addition of urea. These observations indicate that reorganization of compact intermediates involves partial unfolding of the RNA. We find that folding of the ribozyme is most efficient in a mixture of monovalent salt and Mg2+. This is attributed to competition among counterions for binding to the RNA. The counterion dependence of the folding kinetics is discussed in terms of the ability of condensed ions to stabilize compact structures in RNA.
机译：缩合的抗衡离子主要通过减少磷酸基团之间的静电排斥力来增强RNA中紧密结构的稳定性。各种阳离子在四膜虫核酶中引起塌陷状态，该状态在Mg2 +存在下易于转化为催化活性结构。使用天然凝胶电泳来比较平衡离子的价数和大小对这种转变动力学的影响。发现折叠速率随抗衡离子的电荷而降低。单价离子的跃迁比多价金属离子诱导的跃迁快20至40倍。这些结果表明，多价阳离子产生稳定的致密结构，比单价离子诱导的结构更慢地重组为天然构象。在存在亚精胺3+的情况下，其折叠动力学比[Co（NH3）6] 3+快12倍，这与多胺对长距离RNA相互作用的稳定作用减弱有关。在大多数情况下，观察到的折叠速率随抗衡离子浓度的增加而降低。在饱和抗衡离子的量中，通过添加尿素来加速折叠。这些观察表明紧密中间体的重组涉及RNA的部分展开。我们发现，在单价盐和Mg2 +的混合物中，核酶的折叠最有效。这归因于抗衡离子之间竞争结合RNA。折叠动力学的抗衡离子依赖性是根据缩合离子稳定RNA中紧密结构的能力来讨论的。

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